Process of treating asphalt to improve its adhesion



Patented Mar. 23,1954 I UNITED STATES PATENT OFFICE PROCESS OF TREATING ASPHALT TO IMPROVE ITS ADHESION No Drawing. Application August 1, 1950, Serial No. 177,134

6 Claims. (Cl. ltd-273) 1 2 The present invention relates to a process for ing to modify the wetting properties of either the preparation of asphalt-containing compositions asphalt or the aggregate. of improved adhesive properties, and more par- In one method the wetting characteristics of ticularly to a process for combining asphalt with the asphalt and aggregate are altered by treatthe reaction product of a phosphorus sulfide and ,3 ment thereof with water-soluble detergents or water, and to the asphalt-containing reaction wetting agents. A large number of materials product obtainable by said process. have been suggested for this purpose, including The term asphalt as used herein is applied sulfuric acid or aryl sulfonic acid esters of lower to an asphalt suitable for direct use in highway primary alcohols, sulfur compounds, wax, tall oil work, roofing, and also for other purposes and ,1 and oil-soluble water-insoluble heavy metal salts. includes asphalts brought to a consistency de- In another procedure, addition agents, usually sired for a particular use, either by distillation termed additives, are incorporated in the asphalt or by mixing or fiuxing with a harder or a softer in order to improve its wetting properties. A asphalt, as the case may be. The term includes number of such additives have been recom natural asphalt, such as asphaltic rocks, tars and mended in the patent literature, including fats, pitches obtained in the distillation of coal or fatty acids, heavy metal soaps, oleylamine, waxes,

wood, petroleum residues, cracking coal tars, and synthetic or organic compounds having de- The invention is particularly adapted for use tergent or wetting properties. with asphalt from petroleum sources which is However, surface-active agents have in general commonly known as asphalt cement. Asphalt 1 been found to be quite specific, both with respect cement is a highly viscous product obtained by to the ph t ma i l mp y n t the oxidizing or steam-blowing a petroleum residnature of the aggregate surface. A large variety uum to increase its penetration, and the term is of chemically different surfaces are encountered used to distinguish from such a product which is in the average commercial aggr gate, and thus diluted or cut back with a solvent or emulsified 5: such selective action is quite disadvantageous.

with water. The use of such agents has therefore not proved The ability of the asphalt material in bitumito be a p t l xp d ent. nous road matte to resist the action of water is MOTBOVel, 1f the-Se c mpounds are water-soluan important factor in determining the service they have the further disadvantage that y life of th a surface, U l th asphalt 50 are leached out in time by rain which penetrates material shows a strong adhesion to aggregate, the pavement, and after y have ee lost the heavy rains penetrating the matte selectively wet MiheSiVe properties 0f the asphalt aggrethe aggregate and thereby wash the aggregate gate return to their original value. On the other free of asphalt; this eventually tears the pavehand, When the compounds are Water-insoluble, t t, If th adhesion Qf asphalt t agg1'e the increase in adhesion is not as effective as gate were raised to a point above that of water might be desiredto aggregate, the preferential wetting which Aqcordingly, i is an Object of he present inleads to stripping could be prevented and a conventlqn t0 provide a process for Increasing the Siderable saving would result adhesion of asphalt to aggregate.

Moreover predrying the aggregate before lay is a further object O? the lnventi0n to con].- mg the pavement could be avoided In most bine asphalt with an additive in order to permabituminous road construction it is undesirable to nenuy mcrease the adheswn thereof fi remove all water from aggregate so as to Obtain gate Without danger of loss of the additive in strong adhesion when the pavement is initially F laid, because this is an expensive time-consumi is furth? of the g fi g v1 e a process or pro ucing asp a w ch may in rocess. If the as halt-a 1e ate adhesion i greater f' theggwaiepaggregate so used with water-wet aggregate in road mix canrtruction, there i eadhesion, the asphalt would force the water from the g iz avoldmg the need for pr the aggregate surface, selectively displacing it, so

5 It is a further object of the invention to prothat Well aggregate Would be as amenable vide a process for improving the adhesion of ing as dry aggregate. asphalt to aggregate that is simple to employ and Many approaches to this problem have been commercially feasible. employed by the art, but with indifferent success. The adhesion of asphalt to aggregate can be Each method has attacked the problem by seekevaluated by the Ohio State Department of Hiighe to employ dilute aqueous ways Supplemental Specification Test known as The Ohio Test.

In this test the asphalt is evaluated as follows: 100 grams of standard reference stone composed of 50% silica gravel and 50% crushed limestone graded to pass a inch sieve and to be retained on a inch sieve is dried one-half hour at 275 F. and coated with grams of asphalt by mixing with a spatula for three minutes. The mixture is spread thinly on a plate and allowed to cure at a laboratory temperature for one hour. The mixture is then immersed in distilled water at 180 F. for one half hour, after which the number of particles showing stripping is determined. In order to pass the test, the material must show a coating value of at least 95%, i. e., a stripping from not over 5% of the aggregate particles.

In a variation of the Ohio test, the mixture is immersed in distilled water at 212 F. instead of 180 F. for one-half hour. This is a more rigorous test than the regular Ohio test.

Asphalts prepared in accordance with this invention are evaluated by either the Ohio test or the above-described variation thereof.

In accordance with this invention, asphalt which does not meet adhesion requirements of the Ohio test is combined with the reaction product of a phosphorus sulfide and water at a temperature and for a time sufficient to bring the asphalt to an adhesion within the requirements of the said test.

It will be perceived that the objects achieved in accordance with the invention include the provision of economic asphalts of highest quality and their preparation by combining a lower quality asphalt with an additive comprising the reaction product of a phosphorus sulfide and water in an amount to bring the adhesion of the asphalt up to the desired quality standard.

7 Among the phosphorus sulfides which may be 1 reacted with water to produce the additive reacted with asphalt in accordance with the inven tion are tetraphosphorus trisulfide, P4S3, tetraphosphorus pentasulfide, P485, tetraphosphorus heptasulfide, P487, triphosphorus hexasulfide, Pass, and phosphorus pentasulfide, P235. Each of these compounds reacts with water to produce a complex solution containing a large number of reaction products of wide variety. v

The reaction product is formed by combining one mole of the phosphorussulfide with from to 4 moles of water, preferably two moles of water, and then heating the mixture at a temperature in the range of 150 to 350 F. for from to hours, the lower the temperature the longer the time and vice-versa. It is beneficial to carry out the reaction in a closed container under pressure of the gases formed in the course of the reaction, principally hydrogen, phosphine and hydrogen sulfide, but this is not essential. Pressure may be maintained at any desired value, say '70 pounds per square inch, by bleeding off the gases that are formed.

For example, a suitable additive may be prepared from phosphorus pentasulfide by reacting one mole thereof with two moles of water at 250 F. for one hour, maintaining the pressure at 70 pounds per square inch by bleeding on the hydrogen sulfide formed. The reaction product formed by this process is a liquid which has the approximate empirical formula PzSsOz and is a" complex and unique mixture of known and unknown phosphorus and sulfur derivatives in unknown proportions. 7

Instead of employing waterit is also possible acid solution, such as may be formed by dissolving sulfuric, hydrochloric or phosporic acid in water, or dilute aqueous alkali solution, such as may be formed by dissolving sodium hydroxide, calcium oxide or hydroxide or potassium hydroxide in water. All of the above are included in the expression aqueous solution.

The additive prepared as described is blended with the asphalt in an amount in the range of from 0.1 to 2.0% and the resulting mixture heated at a temperature and for a time sufficient to bring the asphalt to an adhesion within the requirements of the Ohio test. The amount depends in part on the asphalt and on the conditions used in preparing the additive.

It has been found in accordance with the invention that maintenance at a temperature in the range of 212 to 500 F. for from 4 to 400 hours, the lower the temperature the longer the time and vice-versa, will increase the adhesion of an asphalt which does not meet the Ohio test adhesion requirement to a'value within this requirement. If a temperature in the range of 300 to 450 F. and a combining time of 12 to. hours are employed, the asphalt will have an adhesion of from 98 to 100%,in the Ohio test, and therefore these conditions are preferred. There is no upper limit to the heating time since after the period has elapsed there is no objection to longer heating.

The additive may be used in any amount that will result in the desired improvement. Generally, the amount falls within the range of 0.1% to 2%, usually 0.25% to 1.0%.

The following examples are of interest in connection with the various methods of preparing the improved asphalt in accordance with the invention.

Example 1 One mole of phosphorus pentasulfide was reacted with one mole of water at 200 F. for 2 hours, at atmospheric pressure. This additive in the amount of 0.25% by weight was added to asphalt from a Mid-Continent crude and the mixture then heated at 300 F. in an atmosphere of carbon dioxide for 336 hours. A 100 gram sample of the reaction product was tested by the Ohio test and a coating value of 100% obtained.

Example 2 One mole of phcs;:horus pentasulfide was reacted with two moles of water at 250 F. for one hour, maintaining the pressure at 70 pounds per square inch by bleeding off the hydrogen sulfide formed. This additive in an amount of 0.5% by weight was added to asphalt from a Mid-Continent crude and then tested by the variation of the Ohio test in which the strippng water bath is maintained at 212 F. instead of 180 F. for one-half hour. coating value was 88%.

The mixture was then heated for 24 hours at 300 F. in an atmosphere of carbon dioxide. At the end of this time the coating value was increased to 94% as nieasured by the same test. After heating the mixture for an additional 72 hours at 300 F. the coating value was 93%.

The results show that the improved result obtained in accordance with the invention is developed only after reaction between the additive and the asphalt, and further that the minimum reaction time at 300 F. is approximately 24 hours.

In contrast, a sample of th asphalt which did not contain an additive gave a value or 65% by the same variation of the Ohio test before heal-tin for be overcome by use of an asphalt having a somewhat higher penetration than it is desired to employ finally.

In the Ohio test the aggregate used is dry. It will, however, be obvious that the invention is not limited to an asphalt to be used on dry stone since the adhesion of the asphalt is improved to such an extent that it will adhere to wet stone or any other surface to be coated with asphalt, such as wood, paper, roofing material, concrete, etc.

It will be noted that there are a number of variables in making the initial phosphorus sulfide-water reaction product and also in making the final asphalt-additive reaction product. These are defined as covering relatively wide ranges, while variations within these ranges result in additives and asphalt compositions of somewhat diiierent properties. They are all effective for improving the adhesion of asphalt, and none of the variables ar critical in this regard.

It will be obvious that in view of the many variables entering into the proces by which the additive-asphalt reaction product is made there are many variations falling within the invention that are not included in the illustrative examples. It is intended that all of these variations are included as fall within the following claims.

' the range of 0.1

All parts and percentages in the specification and claims are by weight.

The term consisting essentially of does not ingredients which do not change the the asphalt composition or ingredients which are essential to the composition. The term thus excludes phosphorus sulfide-olefinwater reaction products.

We claim:

1. A process of preparing an asphalt composition having improved adhesion to aggregate which comprises adding to an asphalt a small amount of an additive consisting essentially of the reaction product of a phosphorus sulfide and an aqueous solution, reacted under non-oxidizing conditions, and heating the mixture of asphalt and additive at a temperature between about 212 and 500 F. for a time of at least 4 hours to improve the adhesion of the asphalt to aggregate.

2. The process of claim 1 in which the phosphorus sulfide is phosphorus pentasulfide.

3. A process in accordance with claim 1 wherein the additive is employed in an amount within 4. An asphalt obtained by the process of claim 1.

5. An asphalt in accordance with claim 4 in which the phosphorus sulfide is phosphorus pentasulfide.

6. The asphalt of claim 4 wherein the asphalt comprises from 0.1 to 2% of the reaction product of phosphorus sulfide and water.

EVERETT C. HUGHES. HARRISON M. STINE.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS OF PREPARING AN ASPHALT COMPOSITION HAVING IMPROVED ADHESION TO AGGREGATE WHICH COMPRISES ADDING TO AN ASPHALT A SMALL AMOUNT OF AN ADDITIVE CONSISTING ESSENTIALLY OF THE REACTION PRODUCT OF A PHOSPHORUS SULFIDE AND AN AQUEOUS SOLUTION, REACTED UNDER NON-OXIDIZING CONDITIONS, AND HEATING THE MIXTURE OF ASPHALT AND ADDITIVE AT A TEMPERATURE BETWEEN ABOUT 212* AND 500* F. FOR A TIME OF AT LEAST 4 HOURS TO IMPROVE THE ADHESION OF THE ASPHALT TO AGGREGATE. 